23-Imino derivatives of LL-F28249 compounds, their preparation and use are described in U.S. Pat. No. 4,916,154. Those compounds are particularly useful for preventing or controlling helminth, ectoparasite, insect and acarid infestations in human and animal health areas.
Various formulations of the 23-E isomer of the 23-(O-methyloxime) of LL-F28249alpha are used worldwide. When preparing those formulations, it is highly desirable to use high purity technical material. However, arduous and time-consuming methods are currently used to increase the purity of technical material containing a 23-E isomer of a 23-imino derivative of a LL-F28249 compound.
U.S. Pat. No. 4,988,824 describes a process for the preparation of 23-(C.sub.1 -C.sub.6 alkyloxime)-LL-F28249 compounds and a method for purifying 23-(C.sub.1 -C.sub.6 alkyloxime)-5-[(p-nitrobenzoyl)oxy]-LL-F28249 compounds. However, the process described in U.S. Pat. No. 4,988,824 occasionally produces product containing the 23-Z isomers of 23(C.sub.1 -C.sub.6 alkyloxime)-LL-F28249 compounds and the purification procedure described therein does not separate the 23-Z isomer from the desired 23-E isomer.
It is therefore an object of the present invention to provide a method for the purification of 23-E isomers of 23-imino derivatives of LL-F28249 compounds which is less arduous, less time-consuming and more efficient than the methods known in the art.